The object of this research project is to evaluate the potential use of electron radiography (ionography) in mass screening for breast cancer. The technique of electron radiography shows great promise in reducing the potential radiation dose received during the course of a screening radiomammographic examination. The following characteristics of an electron radiographic mammography image chamber will be determined: (1) Resolution through measurement of its edge spread function (ESF) and line pair resolution of a gold test pattern. (2) Definition through generation of receiver operating characteristic curvers (ROC) and imaging of a modified Stanton mammography phantom. (3) Cancer detection through comparison with conventional techniques (film and Xeroradiography) of electron mammographic radiographs of suspected neoplastic breast lesions. (4) Sensitivity through measurement using film and thermoluminescent dosimeters of the dose necessary to obtain optimally imaged abnormal breasts.